1. Field of the Invention
The present invention relates to a stencil sheet retaining device for retaining a portion of a stencil sheet at a rotary cylindrical drum so that the stencil sheet, which has already been subjected to a stencil-making process, can be wound around the rotary cylindrical drum in a rotary type stencil printing machine.
The present application is based on Japanese Patent Application No. 2000-035422, which is incorporated herein by reference.
2. Description of the Related Art
In general, the rotary type stencil printing machine has a rotary cylindrical drum capable of rotating around its own axis. A stencil sheet, which has been subjected to a stencil-making process in a stencil making section, is wound on an outer circumferential surface of the rotary cylindrical drum. Inside the rotary cylindrical drum, there is provided an ink supplying device for supplying ink in such a manner that the ink is made to pass through the outer circumferential surface of the rotary cylindrical drum. A pressing type stencil printing is conducted when a printing sheet is supplied to between the rotary cylindrical drum and a roller which comes into contact with the outer circumferential surface of the rotary cylindrical drum. In the stencil printing machine of the aforementioned type, there is provided a stencil sheet retaining device for holding an end portion of a stencil sheet at the rotary cylindrical drum in such a manner that the stencil sheet, which has already been subjected to a stencil-making process, is wound on the rotary cylindrical drum.
A related stencil sheet retaining device is so constructed that a forward end portion of a stencil sheet, which has already been subjected to a stencil-making process and conveyed, can be held by the stencil sheet retaining device. Specifically, the forward end portion of the stencil sheet is held between a magnet plate and a clamping plate made of magnetic material. That is, there is provided an opening and closing mechanism for opening and closing the clamping plate between an attracting position at which the clamping plate, which can be freely opened and closed, is attracted by the magnet plate and a separating position at which the clamping plate is separated from the magnet plate.
The opening and closing mechanism mainly includes a first and a second opening and closing mechanism which will be described as follows.
In the first opening and closing mechanism, an opening and closing angle from an attracting position of the clamping plate to a separating position is approximately 180xc2x0, and the clamping plate is attracted by another magnet plate even at the separating position. At one end of the rotary fulcrum of the clamping plate, there is provided a driven gear. This driven gear is meshed with a drive gear which is moved by a moving device such as a motor or solenoid. When the drive gear meshed with the driven gear is rotated by the drive device such as a motor, the clamping plate can be opened and closed by the rotation of the rotary fulcrum through the driven gear.
In the first opening and closing mechanism, there is provided a protruding type protrusion formed at one end of the rotary fulcrum of the clamping plate. This protruding type protrusion is engaged with a recess type protrusion moved by a moving device such as a motor or solenoid. When the recess type protrusion engaged with the protruding type protrusion is rotated by the drive device such as a motor, the rotary fulcrum is rotated through the protruding type protrusion, so that the clamping plate can be opened and closed.
By the second opening and closing mechanism, the clamping plate is formed like a lever. The clamping plate is usually attracted by the magnet plate (at the attracting position). An operating piece, which is moved by a moving device such as a motor or solenoid, comes into contact with a point of action of the leverage. When the operating piece pushes the point of action of leverage, the clamping plate is put into an open state (at the separate position).
The second opening and closing mechanism has a flapper member, which is opened and closed in the same manner as the clamping plate, at the front portion of the opening and closing end of the clamping plate. The flapper member is also formed like a lever and usually attracted by another magnet plate so that the flapper member is put into closed state. An operating piece, which is moved by the moving device such as a motor or solenoid in a predetermined timed relation, comes into contact with a point of action of the leverage. When the operating piece pushes the point of action of leverage, the flapper member is put into an open state. This flapper member is put into an open state only when the stencil sheet is discharged. Due to the foregoing, when the stencil sheet is set on the rotary cylindrical drum, it is located on an upper side of the flapper member. When the stencil sheet is discharged, the flapper member is put into an open state together with the clamping plate. Therefore, an end portion of the stencil sheet, which is interposed between the clamping plate and the magnet plate, is made to flap from between the clamping plate and the magnet plate, so that the end portion of the stencil sheet can be released.
However, in the above stencil sheet retaining device, the following problems may be encountered. In the first and the second opening and closing mechanism, when a stencil sheet is discharged from and set onto the rotary cylindrical drum, the rotation of the rotary cylindrical drum is once stopped at a predetermined position, and then the clamping plate (and the flapper member) is opened and closed. Therefore, it takes time to discharge the stencil sheet from the rotary cylindrical drum and set the stencil sheet onto the rotary cylindrical drum. Accordingly, it is difficult to reduce a period of time from a stencil-making process to a printing process for obtaining the first printed matter.
As described above, in the first and the second opening and closing mechanism, when the clamping plate (and the flapper member) is opened and closed, the rotary cylindrical drum must be once stopped. That is, when the rotary cylindrical drum is rotated for discharging a stencil sheet, the clamping plate stops holding the stencil sheet and only causes an end portion of the stencil sheet to be free. Therefore, in the related manner, a separation pawl is arranged in the stencil discharging section, so that the free end portion of the stencil sheet can be guided and separated from the rotary cylindrical drum. It is preferable that this separating pawl is located close to the rotary cylindrical drum. However, since the stencil sheet retaining device is arranged, a limit is set when the separating pawl is made to come close to the rotary cylindrical drum. For the above reasons, there is a possibility of the occurrence of failure when the stencil sheet is delivered to the stencil discharging section.
In the first and the second opening and closing mechanism, the clamping plate (and the flapper member) is separated from the magnet plate by a drive force of a motor or solenoid. However, in order to positively hold the stencil sheet, an attraction force of the magnet plate must be sufficiently strong. Therefore, the motor or solenoid, which opens and closes the clamping plate while resisting the strong attraction force, is given a heavy load.
Further, the capacity of the motor or solenoid must be large so that the motor or solenoid can endure the above heavy load. Accordingly, the dimension of the stencil sheet retaining device itself is extended, and the dimension of the entire stencil printing machine is extended. In the first opening and closing mechanism, in order to open and close the clamping plate, it is necessary to provide two driving sources of the moving device and the drive device. Therefore, it is impossible to reduce the dimension of the stencil sheet retaining device and the dimension of the stencil printing machine.
In the first opening and closing mechanism, the following problems may be encountered. Since the opening and closing angle of the clamping plate is large, there is a possibility that an end portion of the stencil sheet, which has been conveyed, is held being bent when it is set onto the rotary cylindrical drum. Due to the foregoing, wrinkles may be caused on the stencil sheet which has been set onto the rotary cylindrical drum, and further the stencil sheet is skewed when it is set onto the rotary cylindrical drum.
In order to solve the above problems, it is an object of the present invention to provide a stencil sheet retaining device, in which a period of time from formation of a stencil sheet to printing can be reduced; a motion of setting the stencil sheet onto the rotary cylindrical drum and discharging the stencil sheet can be stabilized; and a load, which is given to the clamping plate at the time opening and closing the clamping plate, can be reduced.
To achieve the above object, according to the first aspect of the present invention, there is provided a stencil sheet retaining device for holding an end portion of a stencil sheet so that the stencil sheet, which has already been subjected to a stencil-making process, is wound on an outer circumferential surface of a rotary cylindrical drum rotating around own axis thereof. The stencil sheet retaining device comprises: a clamping plate pivotally disposed through a first rotary shaft arranged in parallel with the axis of the rotary cylindrical drum with respect to the outer circumferential surface of the rotary cylindrical drum, the clamping plate having an oscillating end portion which is attracted by a magnet plate arranged at a predetermined position on the outer circumferential surface side of the rotary cylindrical drum so as to hold the end portion of the stencil sheet between the clamping plate and the magnet plate; a flapper member pivotally disposed through a second rotary shaft arranged in parallel with the first rotary shaft with respect to the outer circumferential surface of the rotary cylindrical drum, the flapper member has an oscillating end portion, wherein the end portion of the stencil sheet held by the clamping plate can be located on an upper side on which the oscillating end portion of the flapper member is attracted to the magnet plate; a first contact piece disposed through the first rotary support shaft at an end portion of the clamping plate opposite to the oscillating end portion of the clamping plate; a second contact piece disposed through the second support shaft at an end portion of the flapper member opposite to the oscillating end portion of the flapper member; a cam member having cam grooves movably arranged at a position where the cam member can be contacted with and separated from the first and second contact members, the cam member coming into contact with and pressing the first and the second contact member according to a rotary position of the rotary cylindrical drum, so that the clamping plate and the flapper member can be put into open states in which the clamping plate and the flapper member can be respectively separated from the magnet plate, and so that the open states, in which the clamping plate and the flapper member are respectively open, can be respectively set at a predetermined timed relation and open angle; and a driving device which moves the cam member to positions at which the cam member is contacted with and separated from the first and second contact pieces.
Further, according to the second aspect of the present invention, it is preferable that the flapper member is opened in accordance with rotation of the rotary cylindrical drum due to profiles of the cam grooves of the cam member so as to adjust an open angle of the flapper member, and wherein an end portion of the stencil sheet is drawn out from the clamping plate side which is put into an open state, and the stencil sheet is delivered to a stencil discharging section for discharging the stencil sheet by lifting up the end portion of the stencil sheet so that the end portion of the stencil sheet can be separated from the outer circumferential surface of the rotary cylindrical drum.
Furthermore, according to the third aspect of the present invention, it is preferable that the clamping plate is opened in accordance with rotation of the rotary cylindrical drum due to profiles of the cam grooves of the cam member so as to adjust an open angle of the clamping plate, and wherein an end portion of the stencil sheet conveyed from a stencil making section for making the stencil sheet is guided between the clamping plate and an upper surface of the flapper member.